Pressure adjustable fluid-filled mattresses are well known primarily to prevent bed sores for long-term hospital patients. Hospital beds equipped with mattresses of this type, sometimes referred to as therapeutic beds, typically have a series of transverse bags across the width of the bed filled with pressurized air. The bags are typically arranged into zones so that the air pressure in each zone can be adjusted independently to suit the weight of different parts of the body. The air pressure under the feet, for example, would normally be less than the air pressure under the hips of the patient. The theory behind the bed is that the air-filled bags conform to the shape of the user's body, and support his weight evenly. Unlike conventional beds, bony protrusions experience no more pressure than other parts of the user's body. By eliminating all the high pressure points against the person's body, the chances of developing bed sores is greatly reduced.
At present, most mattresses for therapeutic beds fall into one of two basic categories. In a high air flow mattress, each air bag is connected to a blower at one end, and to an exhaust port at the opposite end. The pressure in each bag can be regulated either by adjusting the air flow rate through an exhaust valve or through an intake valve or both. By constantly cycling air through the bags, any leakage in the bags is easily compensated for, and it is thought that the chances for infection are reduced. Any infectious bacterium or virus, as soon as it enters an air bag, is quickly blown out through the exhaust valve and often filtered out. Such a mattress is shown, for example, in U.S. Pat. No. 4,935,968 to Hunt. The air blower required to operate such a bed must necessarily be quite large, and these beds are often restricted to specially dedicated bed frames which can support the heavy air blower and the complex series of air tubes for the intake, exhaust and filtration systems.
More recently, a low air flow mattress has been developed. In a low air flow mattress, there is no exhaust valve. Instead, air escapes only through the seams and through holes and pores in the air bags. Holes are typically punched in the air bags in specific locations in order to dry the patient's skin and reduce the likelihood of maceration. The medical benefit of this is uncertain. An example of such a bed is shown in U.S. Pat. No. 4,944,060 to Peery. A low air flow mattress still leaks significantly and requires constant blower pressure to all air bags, although the size of the blower and the air flow rate is significantly less than for a high air flow mattress, resulting in a quieter, lighter, and more energy efficient mattress. The pressure in each zone is regulated by intake valves. Excess blower pressure is sometimes released through a bypass waste gate before it reaches the bags.
The existing inflatable air beds present a number of problems, many of which are made worse because the patients who use these mattresses must normally use them for a very long period of time. The constant blower operation necessary to keep the air bags full not only consumes large amounts of electricity, but is a constant annoyance to the patient. It also makes the patient difficult to transport. In order to move the bed to another location, the blower must be coupled to a portable power supply which can be moved along with the bed. Many existing beds require a dedicated bed frame which carries the blower, the tubing, the valves, any control circuitry, and a battery backup power supply. This makes for an expensive, heavy and bulky piece of equipment which is not easy to move. Existing beds also lack a convenient, secure connector for attaching the air bags to a mattress base and, if they can be moved from one hospital bed frame to another, the task is difficult and inconvenient.